The mammalian ras genes encode related, but distinct, 21 kilodalton plasma membrane proteins (P21). A wide range of human and animal tumor cell lines and primary tumors contain structurally mutated ras genes capable of transforming NIH 3T3 cells upon DNA-mediated gene transfer. In an attempt to determine the functions of normal and transforming p21, we shall study the microenvironment of p21 in the membrane and, additionally, identify genes whose products interact with p21 to elicit transformation. Specifically, we shall: (1) Determine the post-translational modification accompanying maturation of p21 to the plasma membrane, and determine the consequences of blocking modification by appropriate site-directed mutagenesis of a ras gene. (2) Characterize the nearest neighbors to p21 in the membrane by introducing purified p21 tagged with photoactivatable crosslinker into living cells. (3) Use DNA-mediated gene transfer to identify genes responsible for the morphological reversion of ras-transformed fibroblasts. (X)